Neutrophil margination, sequestration, and emigration in the lungs of L-selectin-deficient mice

Pulmonary sequestration of polymorphonuclear leukocytes released from bone marrow in bacteremic infection

We examined the bone marrow response and the sequestration of polymorphonuclear leukocytes (PMNs) in lung using a bacteremic infection model in rabbits. PMNs were labeled with the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) in the bone marrow, and the bone marrow release and the sequestration of BrdU-labeled PMNs were measured using immunohistochemistry. A focal subcutaneous infection (S) was induced, and the bacteremia (B) was produced 4 h later with Streptococcus pneumoniae (S+B). This S+B group was compared with other groups with only subcutaneous infection or only bacteremia. The S+B group developed a profound leukopenia after the bacteremia that was associated with an increase in circulating BrdU-labeled PMNs. Morphometric studies showed more PMN sequestration in the lung of the S+B group compared with the others (P < 0.05). Compared with unlabeled PMNs, BrdU-labeled PMNs, which represent newly released PMNs, preferentially sequestered in lung (P < 0.05) and were slow to migrate into the infected tissues (P < 0.05). We conclude that bacteremic infection is associated with an accelerated release of PMNs from the bone marrow and that these newly released PMNs preferentially sequester in lung and are slow to migrate into infected tissues.

Complement Fragment-Induced Release of Neutrophils From Bone Marrow and Sequestration Within Pulmonary Capillaries in Rabbits

Infusion of complement fragments induces rapid sequestration of neutrophils within the pulmonary capillaries. This study examined the contributions of the bone marrow (BM) and the liver to the accumulation of neutrophils within the lungs. Complement fragments induced the release of neutrophils from the BM within 7 minutes of infusion, and these neutrophils sequestered in the lungs immediately upon reaching the pulmonary capillaries. Neutrophils expressing high levels of L-selectin were preferentially retained within the pulmonary microvasculature. By 30 minutes after the infusion was stopped, the circulating neutrophil counts had increased, primarily because of release from the BM. The number of neutrophils sequestered in the lung had decreased by only 27%, and the number of neutrophils in the liver increased by 223%. These studies indicate that complement fragments induce the release of neutrophils from the BM far more rapidly than previously described. These newly released neutrophils immediately sequester within the lung, increasing the number of neutrophils available to injure the lung many fold beyond the number that were circulating before infusion. The preferential retention of L-selectin–expressing neutrophils likely reflects the requirement for L-selectin–mediated adhesion in maintaining sequestered neutrophils within the pulmonary microvasculature. The number of circulating neutrophils reflects a balance between pulmonary sequestration, rapid release from the BM, and uptake by the liver and other organs.

Effect of Sulfo Lewis C on smoke inhalation injury in an ovine model

OBJECTIVE

To evaluate the effect of Sulfo Lewis C (SO3-3âGal1-3GlcNAc-O(CH2)8-COOMe), a putative ligand of selectins, on smoke inhalation injury.

DESIGN

Prospective animal study with concurrent controls.

SETTING

An animal laboratory.

SUBJECTS

Twelve 1-yr-old female sheep, weighing 24 to 33 kg.

INTERVENTIONS

Twelve sheep received nine exposure units of smoke generated by thermolysis of pine woodchips (80 g). Group 1 (n = 6) was untreated. Group 2 (n = 6) was treated with an intravenous infusion of Sulfo Lewis C after smoke exposure. Animals were killed 48 hrs after injury.

MEASUREMENTS AND MAIN RESULTS

Cardiopulmonary variables and blood gases were measured serially. Granulocyte free-radical production was measured before smoke exposure and at 4 and 48 hrs after injury. Ventilation/perfusion distribution (VA/Q) was analyzed using the multiple inert gas elimination technique. Granulocyte free-radical production was increased after smoke exposure in both groups. Oxygenation was significantly improved by the administration of Sulfo Lewis C. VA/Q analysis demonstrated significantly less blood flow to low VA/Q lung segments in treated animals.

CONCLUSIONS

Selectin blockade attenuated lung injury after smoke exposure. These data support the hypothesis that neutrophils play a pivotal role in smoke inhalation injury.

Antibody to E- and L-selectin does not prevent lung injury or mortality in septic baboons

Recruitment of polymorphonuclear leukocytes (PMN) through upregulation of cellular adhesion molecules is a proposed mechanism of injury in sepsis and acute respiratory distress syndrome (ARDS). We hypothesized that pretreatment of baboons with a monoclonal antibody to human E- and L-selectin (EL-246) during sepsis would decrease PMN influx into tissues and result in less organ injury during gram-negative sepsis. We studied 14 anesthetized, ventilated adult baboons; six animals received 1 mg/kg of EL-246 before infusion of an LD100 of live Escherichia coli and six received the E. coli infusion without antibody therapy. Two other animals received 1 mg/kg of EL-246 intravenously without an infusion of bacteria. Intermittent measurements were made of circulatory pressures, cardiac output, urine output, arterial blood gases, ventilation:perfusion ratio (VA/Q), and hematologic status. The experiments were ended at 48 h or at the time of death. Tissues were harvested for pathology and biochemical measurements. The E. coli infusions were associated with a hyperdynamic state, pulmonary hypertension, systemic hypotension, decreased urine output (UOP), and metabolic acidosis. The antibody partly blocked PMN migration, but there were few significant physiologic or biochemical differences between the EL-246-treated and untreated animals. In the antibody-treated animals, UOP was decreased, metabolic acidosis was worsened, and median survival time was decreased significantly. We conclude that treatment with an antibody to E- and L-selectin in gram-negative sepsis does not improve gas exchange or protect against lung injury, and is associated with decreased survival time in primates.

Bacteremic pneumococcal pneumonia: bone marrow release and pulmonary sequestration of neutrophils

OBJECTIVES

Neutrophils have been implicated in the pathogenesis of acute lung injury in bacteremic pneumococcal pneumonia. The characteristics of the population of neutrophils that injure the lung are still not known. This study was designed to compare the bone marrow release and lung sequestration of neutrophils during bacteremic pneumococcal pneumonia with nonbacteremic pneumonia and isolated bacteremia.

DESIGN

Prospective, controlled, experimental study.

SETTING

University research laboratory.

SUBJECTS

Female New Zealand white rabbits (n = 17; weight 2.3 to 2.7 kg).

INTERVENTIONS

The rabbits were pretreated with intravenous 5'-bromo-2-deoxyuridine (BrdU 100 mg/kg i.v.) to pulse label dividing neutrophils in the bone marrow. Twenty hours after the treatment with BrdU, the rabbits were anesthetized and pneumonia was induced by instilling Streptococcus pneumoniae (1.5 x 10(9) organisms) into the lower lobe of the lung. Four hours after pneumonia, bacteremia was induced by infusing S. pneumoniae (3.0 x 10(9) organisms) into the circulation (pneumonia + bacteremia: n = 6). These animals were compared with those with just pneumonia (n = 5) or bacteremia (n = 6).

MEASUREMENTS AND MAIN RESULTS

White blood cell, neutrophil, and differential count. BrdU-labeled neutrophils (neutrophilBrdU) were identified using immunohistochemistry. Cells in tissues were examined microscopically, using sequential level stereologic analysis. The pneumonia + bacteremia group developed a leukopenia (7.3 +/- 0.7 to 2.4 +/- 0.2 x 10(9)/L) following the bacteremia that was associated with an increase in circulating band cells and neutrophilBrdU (2.3 +/- 0.8% to 33.5 +/- 2.8%) which were both higher than those in the other groups (p < .005). Bone marrow smears showed accelerated maturation of neutrophils in the pneumonia + bacteremia group (neutrophilBrdU increased from 11.6 +/- 1.0 to 45.3 +/- 2.1%). Morphometric studies of the lung showed increased neutrophil sequestration in the untreated lung tissue of the pneumonia + bacteremia group (16 +/- 0.8 x 10(8)/mL tissue) compared with the pneumonia (6.6 +/- 0.3 x 10(8)/mL tissue) and bacteremia (12 +/- 0.6 x 10(8)/mL tissue) groups (p < .0001). NeutrophilBrdU preferentially sequester in the lungs of all groups but were slow to migrate into the alveolar air spaces (p < .05).

CONCLUSIONS

During bacteremic pneumococcal pneumonia there is an accelerated maturation of neutrophils in the bone marrow with an enhanced release of neutrophils into the circulation. These newly released neutrophils preferentially sequester in lung microvessels but are slow to migrate into the alveolar air space.

Potential pro-inflammatory effects of soluble E-selectin upon neutrophil function

Appropriate recruitment of neutrophils to sites of infection or tissue injury is a key event in the inflammatory response. A number of studies have shown the critical role of selectins in tethering and rolling of neutrophils on vascular endothelium, as well as a more complex regulatory role, since they have the potential to alter leukocyte recruitment by triggering beta2 integrin-mediated adhesion. In this study, we report that in contrast to patients "at risk" of developing acute respiratory disease syndrome (ARDS), elevated plasma levels of soluble E-selectin are found in patients with established disease. Since neutrophil granulocytes are implicated in ARDS pathogenesis, we have investigated the possibility of a link between elevated soluble plasma E-selectin levels and disease progression by examining the effects of soluble recombinant E-selectin (E-zz) upon neutrophil function. In this paper, we describe the novel finding that exposure of neutrophils to E-zz potentiates a number of neutrophil functions which may act to drive inflammatory processes. Although neutrophil deformability, an important parameter determining retention within the lung microvasculature, was not affected by E-zz, neutrophil polarization was observed. In addition, neutrophil beta2 integrin-mediated adhesion was found to be augmented by E-zz without alteration in levels of surface expression of alphaMbeta2 or the "activation" reporter epitope defined by monoclonal antibody 24. Concomitantly with increased beta2 integrin-mediated adhesion, we observed an inhibition of formyl-Met-Leu-Phe-directed chemotaxis. Together with an augmentation of neutrophil reactive oxidant species production and release of superoxide anions, these data raise the possibility that soluble E-selectin exerts pro-inflammatory effects upon neutrophil function at sites of inflammation, thereby exacerbating disease processes.

Role of CD18-ICAM-1 in the entrapment of stimulated leukocytes in alveolar capillaries of perfused rat lungs

This study aimed to examine the behavior of stimulated leukocytes in the pulmonary microcirculation. The leukocyte-endothelium interaction was visualized under physiological shear rates in perfused rat lungs using high-speed confocal laser video microscopy. Leukocytes labeled with carboxyfluorescein were stimulated with cytokine-induced neutrophil chemoattractant (CINC/gro), which caused L-selectin shedding and inverse upregulation of CD18. Neither unstimulated nor stimulated leukocytes exhibited rolling in either pulmonary arterioles or venules, whereas both were sequestered in capillaries. Approximately 50% of stimulated leukocytes showed a transient cessation of movement in pulmonary capillaries. The CINC/ gro stimulation, which inhibited leukocyte rolling and adhesion to mesenteric venules, reduced leukocyte velocity and increased leukocytes in pulmonary capillaries. Pretreatment with monoclonal antibodies against intercellular adhesion molecule-1 (ICAM-1) or CD18 attenuated these changes. Confocal microfluorography revealed constitutive expression of ICAM-1 not only in venules but also abundantly in capillary networks. These results suggest that selectin-independent, CD18-ICAM-1-dependent capillary sequestration is one of the major mechanisms by which activated leukocytes accumulate in the lungs.